"Waterless" cooking is old, as are knobs which give an audible signal when steam is formed to indicate attainment of cooking temperatures. Tops for cooking vessels which are provided with whistles and having means to turn the whistle off or to allow the escape of steam are also known. However, mechanically these are quite different from my device. Many such knobs cannot be disassembled. Those few which can be disassembled for cleaning could also release the knob portion accidently under steam pressure, which might well cause loss of the knob or even injury. The present invention has the advantage over my previous invention U.S. Pat. No. 4,418,637 (Heermans) in that the current valve assembly allows the opening in the lid of the cooking vessel to be substantially reduced preventing accidental insertion and injury of the user's finger or fingers during assembly or disassembly.